The present invention relates to replaceable abrasive pads for ophthalmic lens lapping tools used for fine grinding of glass or plastic lenses.
Generally speaking, optical lens surfacing is conventionally carried out by first grinding an approximate curve into the lens by means of a grinding wheel on a curve generator. Then the exact optical curvature of the lens is abraded using a lens lapping tool having a surface characterized by having the optical curvature desired for the lens itself. For glass lenses, the required abrasive is generally provided by continuously feeding a loose abrasive slurry between the lens and the lens lapping tool. This procedure yields a lens with a curve and finish that can be readily polished to achieve a lens of optical quality. For plastic lenses, the abrasive is provided by using a sandpaper pad of the wet or dry type on the surface of the lens lapping tool and grinding lubricant is provided by flowing water between the lens and the sandpaper pad. Both glass and plastic lenses are polished with a velvetine or felt pad on the lens lapping tool using a tin oxide or cerium oxide compound in water as a polishing agent.
Lens lapping tools are relatively expensive because of their precise nature and the requirement of a different lapping tool for each curvature desired in the lens product. Hence, abrasive shims or pads have been developed in the art for use between the lens lapping tool and the lens surface in order that the shim or pad will wear rather than the lens lapping tool itself. Examples of facings or pads for lens grinding tools are disclosed, for example, in U.S. Pat. Nos. 3,144,737, Aug. 18, 1964 to Faas, 3,324,608, June 13, 1967 to Hoenig, 3,522,680, Aug. 4, 1970 to Sarofun, 3,594,963, July 27, 1971 to Beasley, 3,699,721, Oct. 24, 1972 to Beasley, 3,921,344, Nov. 25, 1975 to Goodwin, and 4,019,289, Apr. 26, 1977 to Korrer. U.S. Pat. No. 3,959,935, June, 1, 1976, to Stoppacher discloses an abrasive pad for grinding lenses having an abrasive substance on its surface so that no abrasive slurry must be employed to effect grinding of lens blanks. U.S. Pat. No. 4,047,902, Sept. 13, 1977 to Wiand, discloses a generally useful abrasive product.
Conventional pads, however, wear quickly and must be replaced every cycle, i.e. after each lens is ground, which involves down time on equipment and is generally inconvenient and disruptive to the lens grinding process. Hence, it would be desirable to be able to provide an abrasive pad having a wear resistant, abrasive surface such as is provided by diamond particles metal plated thereon for use in abrading optical lenses. But it has heretofore been thought impractical to use diamond abrasive coated pads for grinding lenses because in previous attempts, they tended to impart scratches to the lens surface. Lapping pads generally have a plurality of radially extending channels cut through the area of the pad so that the pad can conform to the surface of the lens lapping tool. It is believed that during the metal plating of the diamond abrasive particles on the surface of the lapping pad, a significant degree of build-up or "over-plating" occurs along the perimeter of the pad surface. The plurality of radially extending channels cut in the pad and required in order for the pad to conform to the curved surface of the lens lapping tool have the effect of greatly increasing the length of perimeter edges subject to overplating and hence the tendency of the pad to scratch the lens surface.
Thus, it is an object of the present invention to provide a method of making an ophthalmic lens lapping pad which does not require an abrasive slurry during use and which is characterized by having an abrasive surface of diamond particles metal plated thereon. It is another object of this invention to provide a diamondcoated lens lapping pad which can be used to abrade a lens blank without imparting scratches thereto. It is a further object of the present invention to provide a lens lapping pad which has a long life in service and is more economical to use than conventional pads.
These and other objects will be apparent from the following disclosure of the present invention which involves first metal plating diamond abrasive particles onto a sheet substrate and then cutting lens lapping pads therefrom in shapes adapted to conform to the curved surface of a lens lapping tool.